What is an ultrasound exam and why does my veterinarian recommend it for my pet?

Ultrasound is a valuable and non-invasive way to image internal organs and soft tissues. Ultrasound utilizes soundwaves at high frequencies that are not audible. They are sent into the tissue via a small hand-held probe. Various tissues and organs reflect soundwaves differently due to difference in water content and physical properties. The returning echo is absorbed by the ultrasound probe, and the software of the ultrasound machine processes the echo data and then makes a picture. At first, an ultrasound image looks like a jumble of grey shades, but with knowledge of the anatomy and normal architecture, and training of the human brain to recognize patterns, the doctor performing and interpreting the ultrasound exam can see the organs and learns to differentiate normal from abnormal and can therefore diagnose many types of diseases.

So, in summary, ultrasound is a non-invasive, relatively inexpensive imaging technique (when compared to the cost of a CT scan or MRI). It requires extra post-veterinary-graduate training and multiple years of experience to perform high-quality ultrasound exams.

Doctors typically gain a lot of information from an ultrasound exam.
Importantly, if an ultrasound exam is reported to be normal, this is also valuable information for the doctor and, of course, good news for the pet owner.

Presenting clinical signs, exam findings, radiographic or laboratory abnormalities that often lead to the recommendation for an ultrasound exam:
- vomiting and diarrhea that does not go away with medical treatment, concern for foreign objects in the gastrointestinal tract that are not visible on radiographs, concern for an intestinal obstruction
- decreased appetite and inappetence
- increased/ravenous appetite
- unexplained weight gain or abdominal distention (often pet owners will note a “bloated stomach” or “increased size of the belly”)
- unexplained weight loss
- increased water intake and/or urination, pet owners often complain about “urinary accidents in the house”
- increased frequency of urination, straining or painful urination or defecation
- blood in stool
- urine leakage while sleeping or walking (incontinence)
- weakness
- abdominal pain
- fever without an obvious cause
- abnormal swelling on ventral neck – concern for thyroid or other tumors of the neck structures
- geriatric pets are checked for cancer or other disease that cause changes to organs
- palpable mass in abdomen on exam
- abdominal pain that cannot be explained and persists
- heart murmur on exam
- clinical concern for heart disease such as coughing, increased respiratory rate and effort, and collapsing events
- radiographic abnormalities that require additional information such as an enlarged heart, fluid in the chest, possible tumor in abdomen, abnormal shape and contour of organs, mineralizations, possible foreign objects, etc.
- laboratory abnormalities that require additional information about organ architecture such as elevated liver enzymes, elevated bilirubin (hyperbilirubinemia), elevated kidney values (azotemia), high blood calcium (hypercalcemia), low blood protein (hypoalbuminemia), low blood glucose (hypoglycemia), elevated BNP (concern for heart disease), abnormal cancer blood test (Nu.Q cancer test), abnormal cell counts (high or low red and white blood cells, low platelets), etc.

Diseases that are commonly diagnosed with ultrasound:
- Tumors/nodules (growths) – ultrasound cannot differentiate if a tumor is bad/malignant (cancerous) or good/benign (non-cancerous). With experience, it is possible to sometimes suspect if a tumor is malignant based on certain criteria such as vascularity, size/shape, evidence of invasion of surrounding tissues, and other changes, but further testing is often needed to definitively diagnose or rule out cancer when a tumor or nodule is found on ultrasound exam. Often the options are to obtain a sample, which is mildly invasive and not always conclusive (fine needle aspirate, needle biopsy), perform blood or urine testing (only possible for some cancers), or repeat the ultrasound a few weeks or months later to monitor the growth rate of a tumor or nodule. If a tumor/growth is an incidental finding, it is often fair to take a wait and recheck approach, but if a tumor is suspected to cause clinical signs or expected to cause problems (e.g. bleeding into the abdomen), further testing such as CT scan, biopsy or surgery may be the recommended next steps.
- Congenital anomalies – abnormalities of organs that animals are born with that could impact quality of life, e.g. portosystemic shunt and other vascular (blood vessel) anomalies, ectopic ureter (abnormal insertion of the ureter into the urethra), heart abnormalities (many types), etc. Some of these abnormalities can be corrected with surgical procedures while some are managed medically.
- Foreign objects in the intestinal tract (stomach or intestine) that are not visible on radiographs and are possibly causing problems such as vomiting and obstruction of the intestine
- Gallbladder disease (e.g. mucocele, stones, cholecystitis) and obstruction of the bile duct
- Chronic degenerative disease that causes changes to organ architecture, e.g. chronic kidney disease
- Fluid accumulations in body cavities, fluid accumulation in organs and soft tissues (e.g. cysts, abscess, etc.)
- Inflammation of the pancreas (pancreatitis)
- Stones in the gallbladder, bile duct, liver, pancreas, and urinary tract (kidney, ureter, urinary bladder)
- Atrophy/shrinkage of organs with reduction of function (e.g. chronic kidney disease, adrenal atrophy due to a contralateral tumor or Addison’s disease)
- Hypertrophy/enlargement of organs due to various diseases (e.g. lymph nodes, prostate, liver, kidneys, adrenal glands)
- Abnormal wall of the stomach or intestines due to gastrointestinal disease (e.g. gastritis, enteritis, inflammatory bowel disease, lymphoma, other types of cancer)
- Blood clots (thrombus) in larger blood vessels (e.g. aortic thromboembolism, portal vein thrombus, etc.), vascular dilation (e.g. caudal vena cava dilation secondary to right sided heart disease) and abnormal blood vessel walls (e.g. atherosclerosis), portal vein dilation and decreased flow velocity due to portal hypertension

Ultrasound is especially great to evaluate the heart for many types of heart diseases and to monitor the progression once heart disease was diagnosed. This study is typically called echocardiogram and involves not only 2-D imaging of the heart and measurements of the chambers and wall thickness but also assesses blood flow across valves and through the chambers, the function of the heart muscle and pressure gradients between chambers and the peripheral blood vessels with various additional imaging techniques. Follow this link to learn more about the common types of heart diseases found in cats